1. Field of the Invention
This invention relates to the use of a novel ansa macrolide compound useful as an agent for the control of insect pests.
2. Description of the Prior Art
The isolation of three ansa macrolides from ethanolic extracts of Maytenus ovatus and Maytenus buchananii was first reported by S. M. Kupchan et al. and is the subject of U.S. Pat. No. 3,896,111. These maytanside esters are characterized by the structural formula ##STR2## and include maytansine in which R.dbd.CH.sub.3, maytanprine in which R.dbd.CH.sub.2 CH.sub.3, and maytanbutine in which R.dbd.CH(CH.sub.3).sub.2. Kupchan reports that these compounds showed activity against lymphocytic leukemia P388 in test animal tumor systems. Two analogs of maytanbutine isolated from Colubrina Texensis are taught by Wani et al. [J.C.S. Chem. Commun., page 390 (1973)] in which the C-15 position bears either an hydroxyl (colubrinol) or an acetate (colubrinol acetate) side chain. These compounds have also demonstrated activity against lymphocytic leukemia P388, and in addition show cytotoxicity (ED.sub.50) against KB cell culture. In a later publication by Kupchan et al. [J. Org. Chem. 42: 2349-57 (1977) ] a variety of maytansinoids are reviewed and are categorized as either maytanside esters (those having a C-3 ester side chain) or as maytansides (those lacking the C-3 ester side chain). Of particular significance is the disclosure of finding yet another antileukemic principle, maytanbutacine. This maytanside ester was isolated from Maytenus serrata and is similar to colubrinol acetate in that it has an acetate side chain in the C-15 position. The difference lies in the C-3 ester group, which is ##STR3## This reference also teaches the isolation of maytansine and related compounds from another celastraceous plant, Putterlickia verrucosa. In U.S. Pat. No. 4,190,580, Hashimoto et al. shows that the maytansinoids are also useful as antifungal and antiprotozoan agents.
Higashide et al. [Nature 270: 721-722 (1977) and U.S. Pat. No. 4,225,494] and Asai et al. [Tetrahedron 35: 1079-85 (1979)] first reported the recovery of ansamitocin, a group of ansamycin antibiotics from a fermentation broth of Nocardia sp. No. C-15003 (N-1). The structures of the compounds are similar to maytansine, differing only with respect to the C-3 moiety. Ansamitocin demonstrated strong growth inhibitory activities against phytopathogenic fungi, dermatophytes, and protozoa. Two of the compounds also possess antitumor activity against the P388 strain, as well as significant activity against B16 melanoma, sarcoma 180, Ehrlich carcinoma, and P815 mastocytoma. Some activity was also shown against leukemia L1210.